This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The recent approval by the FDA of the quadrivalent meningococcal conjugate vaccine (MCV4) has led to a recommendation to vaccinate 11-12 year-old individuals at a pre-adolescent visit, individuals entering high school (approximately 15 years of age) and incoming college freshman living in dormitories, in recognition of the increased meningococcal disease risk during adolescence. As the majority of children with perinatally acquired HIV infection have aged into adolescence, and the majority of new pediatric HIV infections in the US are occurring in the adolescent age group, the new age-based recommendations for meningococcal immunization patients will lead to most HIV-infected youth being age-eligible for a vaccine for which there are no safety or immunogenicity data available from HIV-infected populations. This phase I/II study will evaluate the safety and immunogenicity of MCV-4 in 296 HIV-infected youth between \u8805?11 and <25 years of age. This study is also designed to answer several important questions related to immunization of HIV-infected youth including both short-term and long-term immunogenicity. The primary objectives are: To compare the immunogenicity of the MCV4 in HIV-1 infected youth at 28 weeks between a single-dose regimen vs. a two-dose regimen, where an immunogenic response is defined as a 4-fold or greater increase in serum bactericidal antibody titers;To estimate the short-term (4 and 24 weeks) immunogenicity of the MCV4 vaccine in HIV-1 infected youth for those in Group 1 (CD4% \ul >\ulnone 15);To estimate the long-term (at 72 weeks) immunogenicity of the MCV4 vaccine in HIV-1 infected youth;To evaluate the safety of the MCV4 vaccine in HIV-1 infected youth, including short-term local and systemic reactions following administration of the vaccine. HYPOTHESIS MCV-4 immunization in HIV-infected youth will be safe and the vaccine will be immunogenic in a single dose regimen for youth who have CD4% >\ but two doses will be required for immunogenicity in youth who have CD4%<15. SPECIFIC AIMS To compare the immunogenicity of the quadrivalent meningococcal conjugate vaccine (MCV4) in HIV-1 infected youth at 28 weeks between a single-dose regimen vs. a two-dose regimen, where an immunogenic response is defined as a 4-fold or greater increase in serum bactericidal antibody titers; To estimate the short-term (4 and 24 weeks) immunogenicity of the MCV4 vaccine in HIV-1 infected youth for those in Group 1 (CD4% \ul >\ulnone 15); To estimate the long-term (at 72 weeks) immunogenicity of the MCV4 vaccine in HIV-1 infected youth; To evaluate the safety of the MCV4 vaccine in HIV-1 infected youth, including short-term local and systemic reactions following administration of the vaccine. To examine whether the short and long-term immunogenicity of the MCV4 in HIV-1 infected youth varies as a function of the study subjects'immune status at the time of vaccination; To compare the long-term immunogenicity (at 72 weeks) of the MCV4 in HIV-1 infected youth between a 1-dose vs. 2-dose regimen for those in Group 1 (CD4% \ul >\ulnone 15) To evaluate whether the safety of the MCV4 vaccine varies by immune status based on CD4% at the time of vaccination; To evaluate whether, in subjects with CD4% <15%, 2 doses of MCV4 can produce an immunogenic response (defined as a 4-fold or greater increase \cf0 in serum bactericidal antibody titers\cf2 reaching at least 1:8); To identify host genetic determinants of immunity that may affect\b \b0 the response to MCV4.